ive had that problem with using some older usb keyboards . something i use is the usb to ps/2 adapter for my keyboard and it detects it instantly. I still use this setup on my rig since im using an older keyboard which may be the problem. that or you may have to try and original keyboard with a ps/2 and pop into the bios to change some usb settings, sometimes thing are disables in the newer bios to detect usb hardware after boot so it doesnt try to boot them like a usb drive. pretty weird compared to the older bios'